TAXONOMIC CHARACTERISTICS OF SPHENOPHYLLALEAN CONES

The range of variability in the taxonomic characteristics traditionally used to establish genera and species of Sphenophyllum cones is studied from specimens of Bowmanites dawsoni, B. trisporangiatus, B. bifurcatus, Litostrobus, and Sphenostrobus. Taxonomic criteria examined include configuration of the cone stele, number of sporangiophores per bract, anatropous vs. orthotropous sporangium attachment, number of appendages per node, and spore morphology. Because of the large degree of variability observed, these characteristics do not appear to adequately differentiate between the genera Litostrobus and Sphenostrobus, so these genera are combined under Sphenostrobus. A new combination, S. iowensis, is proposed for specimens previously described as L. iowensis, L. paulus, and B. moorei. It is suggested that species currently placed in the genus Bowmanites may represent several distinct natural genera of sphenophyllalean cones.